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Growth Hormone

Test Overview

A growth hormone
(GH) test measures the amount of human growth
hormone (GH) in the blood. GH is made by the
pituitary gland and is needed for growth. It plays an
important role in how the body uses food for energy (metabolism).
The amount of GH in the blood changes during the day and is affected by
exercise, sleep, emotional stress, and diet.

Too much GH during
childhood can cause a child to grow taller than normal (gigantism). Too
little GH during childhood can cause a child to grow less than normal (dwarfism). Both conditions can be treated if found
early.

In adults, too much GH is caused by a noncancerous tumor
of the pituitary gland (adenoma). Too much GH can cause bones
of the face, jaw, hands, and feet to grow larger than normal (acromegaly).

Growth hormone can cause the
release of other substances (factors) that affect growth and metabolism. One of
these is
insulin-like growth factor 1 (IGF-1). When the GH
level is very high, the IGF-1 level is also very high. A test for IGF-1 may
also be done to confirm high GH levels.

Why It Is Done

A test for growth hormone (GH) is done
to:

See whether a child whose growth is abnormal
has dwarfism or gigantism.

See whether an adult has acromegaly.
This condition is caused by a tumor (adenoma) of the pituitary
gland.

Check treatment that uses growth hormone.

How To Prepare

No special preparation usually is required before having this test. Be sure to tell your doctor about all the nonprescription and prescription medicines you take.

How It Is Done

Blood levels of growth hormone (GH) can
change quickly, so more than one blood sample may be taken on different days.
Insulin-like growth factor 1 (IGF-1) levels change more slowly, and it may be
the first test done.

The health professional drawing blood
will:

Wrap an elastic band around your upper arm to
stop the flow of blood. This makes the veins below the band larger so it is
easier to put a needle into the vein.

Clean the needle site with
alcohol.

Put the needle into the vein. More than one needle stick
may be needed.

Attach a tube to the needle to fill it with
blood.

Remove the band from your arm when enough blood is
collected.

Put a gauze pad or cotton ball over the needle site as
the needle is removed.

Put pressure on the site and then put on a
bandage.

How It Feels

The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
pinch.

Risks

There is very little chance of a problem from
having a blood sample taken from a vein.

You may get a small bruise at the site. You
can lower the chance of bruising by keeping pressure on the site for several
minutes.

In rare cases, the vein may become swollen after the
blood sample is taken. This problem is called phlebitis. A warm compress can be
used several times a day to treat this.

Ongoing bleeding can be a
problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and
other blood-thinning medicines can make bleeding more likely. If you have
bleeding or clotting problems, or if you take blood-thinning medicine, tell
your doctor before your blood sample is taken.

Results

A growth hormone (GH) test measures the
amount of human growth
hormone (GH) in the blood.

Normal

The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what's normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.

High values

High GH values may mean
gigantism or
acromegaly is present. These conditions are caused by
a noncancerous tumor in the pituitary gland (adenoma). Insulin-like growth
factor 1 (IGF-1) levels should also be high.

High GH levels may also
be caused by
diabetes, kidney disease, or starvation. These
conditions do not cause high IGF-1 levels.

What Affects the Test

Reasons you may not be able to
have the test or why the results may not be helpful include:

What To Think About

Normal levels of growth hormone (GH) change
during the day so other tests may be done to confirm the results of a GH test.
Other tests can show whether low levels of GH (which can be normal) mean the
pituitary gland is not working correctly.

The growth hormone suppression test (also called the
glucose loading test) measures the level of GH in the blood before and after a
person drinks fluid with a large amount of sugar (glucose) in it. Normally, the
amount of GH drops to less than 1 ng/mL after drinking the glucose. Levels of
GH that stay high may mean acromegaly is present.

The growth
hormone stimulation test measures the level of GH in the blood before and after
insulin or arginine is given in a vein (intravenously)
in the arm. No detectable growth hormone can be found for people with normal pituitary function. A growth hormone
stimulation test may be used to see if a person lacks GH. Normally, the amount
of GH increases after insulin or arginine. A GH level that does not increase
after the insulin or arginine is given may mean the person lacks growth
hormone.

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